1. Field of the Invention
The present invention relates to organic resin compositions, and more particularly to hypoallergenic and substantially non-toxic environmentally safe organic resins and a method for preparing the same, the method including polymerizing a very low toxicity cycloaliphatic bicyclic epoxy with a nontoxic functional carboxylic acid vegetable oil through incorporation of a non-toxic hypoallergenic catalyst.
2. Background of the Invention and Prior Art
Because of their low cost and abundant availability, resins from the polyester family are used in a variety of manufacturing industries. For instance, the production of fiberglass typically uses polystyrene or polyamine/epoxy curing systems. However, during fiberglass production, it is well known that there are typically high emissions of volatile organic compounds (“VOCs”). For instance, for fiberglass boat manufacturing alone, the total national VOC emissions is estimated to be 20,150 tons per year (U.S. Environmental Protection Agency, Assessment of VOC Emissions from Fiberglass Boat Manufacturing, May 1990, EPA-600/2-90-019. EPA's Control Technology Center at Research Triangle Park, N.C., Charles H. Darvin Project Officer). Much of the emissions are acetone and styrene. Because of the low cost of using a resin from the polyester family, their use is commonplace despite the release of environmentally damaging emissions.
Many of these polyester resins are prepared from dicarboxylic acids and difunctional alcohols, wherein the two are reacted together to create a chain comprising ester linkages. Double bonds are incorporated by reacting maleic anhydride into the polymer chain and the molecular weight is adjusted by controlling the ratio of reactants to keep the chain in liquid form for processing purposes. The chains are then linked together with styrene. A radical initiator is used to activate the styrene for reaction with the maleic double bond. When the first reaction occurs, the free radical transfers to and opens the maleic double bond, where it then reacts with the styrene double bond, opening it up to put a free radical on the styrene which then undergoes reaction with the maleic double bond as before. This continues until all the chains are linked together and/or all the styrene is consumed.
A first drawback to this means of production is that excess styrene can cause the resin matrix to become very brittle and easily broken. The styrene is also volatile, foul smelling, and toxic. Any facility preparing significant quantities of material must be extremely well ventilated, and workers generally wear a chemical respirator or use a fresh air breathing system. Even if the use of excess styrene is avoided, when this process is used to make reinforced fiberglass composites, bending loads on the cured composite can still easily make the polyester craze and crack. Finally, resin systems made under these conditions break down under ultraviolet (“UV”) light due to unwanted free radical formation, ultimately resulting in a shorter lifespan for the fiberglass composite.
A second drawback relates to alterations in the cure rate of the resin. To alter the cure rate of an amine epoxy resin, the conventional method used by a manufacturer involves altering the concentration of the polymerization catalyst. Polyester based systems currently in place employ a radical initiator for the creation of reaction sites and hence if more initiator is present more reaction sites are present and the reaction runs faster. However, this also leads to shorter polymerized chains and increased cross-linking, leading in turn to a more brittle product. Unlike catalysts, initiators are consumed by the reaction. There is therefore a need for a resin with an adjustable rate of cure, wherein adjustments to the rate do not lead to adjustments in the final properties of the cured resin.
Despite these drawbacks, conventional polyester resins remain popular because they use relatively inexpensive components and are easy to apply to many applications.
The second commonly used type of resin is an amine-epoxy resin, generally comprising an aliphatic amine backbone. Resins of this type are versatile, autocatalytic (that is, the catalyst and the curing agent are one and the same) and can form polymer structures with a wide range of properties. However, to realize these wide-ranging properties, it is necessary to use an array of amine curing agents. Most common amine-epoxy systems utilize an epoxy resin produced from a reaction between epichlorohydrin and bisphenol A. Consequentially, it is not necessary to modify the epoxy structures to alter the characteristics of the end products. Instead, the amine-curing agent is generally changed, as described below. The downside of these epoxy resins is the toxicity and carcinogenic properties of the epichchlorohydrin. Indeed, in order to keep the epoxy resin from being classified as a carcinogen, manufacturers must remove excess residual epichlorohydrin. Finally, both epichlorohydrin and bisphenol A are suspected endocrine disruptors.
The aliphatic amine-curing agent for a typical amine-epoxy resin generally consists of linear chains having recurring secondary amine groups in-line every two-carbon atoms. The difference among these aliphatic amine-curing agents usually is the number of these two-carbon groups in the chain. The ends of these chains contain primary amines, which are far more reactive toward the epoxy resins than are the secondary amines along the chain. This usually means that the reaction with epoxies is fairly rapid until the primary amines have reacted. The reaction rate then slows down as the reaction continues with the secondary amines.
There are several undesirable aspects to the aliphatic amine curing agents. They usually have fair volatility and a strong disagreeable odor. The fumes and amines themselves are toxic and can cause skin irritations. These resin systems usually cure to a hard brittle stage, and, if not formulated properly, will continue to harden. Over time this can cause a significant change in properties in the final composite.
An additional negative characteristic of amine/epoxy resin systems is that the rate of the reaction cannot be changed without also changing the amine. The amine epoxy is self-catalyzing, so to change the reaction rate, the amine must be changed. For instance, for faster reactions, low molecular weight, fast reacting amines such as aliphatic amines, including ethylene diamine or diethylene triamine, may be used. This is because the terminal amine groups are primary amines, which react faster. The secondary amines react slower, thus, the longer the chain, the greater the concentration of secondary amines and the slower the reaction. Thus, for slower reactions, diethyl amines or other secondary amines may be used. Changing the amine, however, changes the properties of the final product. Additionally, like the polyester resin, the amine/epoxy resin is degraded by UV light, undergoing amine oxidization under UV exposure due to radical attack at the amine portion of the polymer, this amine oxidization goes on to cause chalking Finally, because the catalyst and the curing agent are one and the same, as the reaction progresses and the curing agent hardens, the amines and, thereby the catalysts are rendered more and more immobile.
An additional negative characteristic of both resins (polyester and amine-epoxy) is that during the course of curing, both resins exhibit undesirable cure shrinkage. Much effort has gone into reducing this shrinkage in order to produce end products that are truer to the mold on which they are based. A final downside to both resins is their elongation properties. Specifically, the amine/epoxy resin only provides for 5.0% elongation before breaking. The polyester system has even less at only 2.45% elongation before breaking.
In summary, there are thus several downsides to the above systems, including but not limited to shrinkage upon curing, poor elongation characteristics, degradation upon UV light exposure, brittleness, limited range of cure rates, and the release of harmful VOCs during production. There is thus a need for a hypoallergenic, substantially non-toxic, environmentally friendly resin that overcomes the above disadvantages.
One solution is found in recently developed epoxy resin systems that utilize cycloaliphatic-curing agents. The addition of cycloaliphatic curatives in the hardener or curing agent of epoxy resin systems greatly improves the epoxy. Cycloaliphatics are known for their improved weather resistance, tolerance to water and moisture, resistance to blushing and water spotting and better chemical resistance. In addition, they provide better impact resistance. As a downside, these new solutions are expensive, enough so that often the traditional resins are still used, despite their downsides.
It is thus an object of the present invention to provide a hypoallergenic, substantially non-toxic, environmentally friendly resin system that limits obnoxious odors, irritating fumes, and VOCs while exhibiting wide ranging cure rates and capabilities.
It is a further object of the present invention to provide a resin system wherein the final cured properties of the resin remain the same despite modifications to the rate of cure.
It is a still further object of the present invention to decrease employee exposure to toxic chemicals and thereby strongly impact the growth for small business that might otherwise be overwhelmed by the huge capital costs normally associated with meeting all the safety guidelines applied to the use of conventional composites.
It is a further object of the present invention to provide a resin that is not brittle or easily broken, that exhibits excellent elongation properties, and that does not significantly shrink during the course of resin curing.